Defect annealing in Mn/Fe implanted TiO2 (rutile)H. P. Gunnlaugsson on behalf of the Mössbauer collaboration at

ISOLDE/CERN (IS501)

• Motivations• Experimental• Results• Discussion/conclusion

2

TiO2 (rutile) motivations

Very radiation hard: Can only be made amorphous by implantation at T < 77 K or extreme fluences (>>1 dpa)Possible host for upconversionReports on dilute magnetism

O2-

Ti4+

Er3+: ZnO, TiO2, …

3

Experimental57Mn for 57Fe Mössbauer spectroscopy

General principle:

Implantation of short lived parent isotopes

57Mn (1.5 min.)

57Fe

Resonancedetection

g

Major benefits- Fe charge state (Fe3+/Fe2+)- Fe site symmetry- Fe3+ spin relaxation

- High dilution ~10-4 at.%- Creation of defects

ER ~ 40 eVER,max = 93 eV

Mössbauer spectroscopy/Hyperfine interactions: Sensitive only to nn – nnn effects

4

Results: Temperature series

-12 -8 -4 0 4 8 12

329 K

357 K

477 K

541 K

603 K

662 K

-12 -8 -4 0 4 8 12

143 K

182 K

220 K

262 K

305 K

315 K

Fe2+

SL

-12 -8 -4 0 4 8 12

329 K

357 K

477 K

541 K

603 K

662 K

Velocity (mm/s)

Rel

ativ

e em

issi

on (a

rb. u

nits

)

-12 -8 -4 0 4 8 12

143 K

182 K

220 K

262 K

305 K

Dominated by Fe2+ speciesSingle line (SL) component at highest T’sSomething on the wings… consistent with slow relaxing paramagnetic Fe3+

SL due to Fe3+

5

Results: Angular dependence

-12 -8 -4 0 4 8 12

Rel

ativ

e em

issi

on (a

rb. u

nits

)

Velocity (mm/s)

q = 80 �

q = 60 �

q = 0 �

T = 143 K

-12 -8 -4 0 4 8 12

Rel

ativ

e em

issi

on (a

rb. u

nits

)

Velocity (mm/s)

q = 80 �

q = 60 �

q = 0 �

T = 220 K

Clear angular dependenceFe2+ can probe the lattice structure through the quadrupole interaction

6

Results: Spectral area

Pure TiO2: Fe as Fe3+

+ Oxygen vacancies (VO)

Fe2+

+ Titanium vacancies (VTi)

Fe3+(/4+)

0102030405060708090

100

100 200 300 400 500 600 700

Are

a fr

actio

n (%

)

Temperature (K)

Fe(II)

Fe(III) + SL

Fe2+/3+

VO

VTi

Fe2+/3+

VO

VTi

Fe2+

VO

Fe2+ Fe3+

7

Pair disociation

Probability of dissociation:

)ln(½)(1

)(

0AA

0

0

kTETpe

eTpkT

E

kTE

Complex: Diss. Energy Binding energy [Navarro et al., 2011] (theory)

Mn – VO: 1.60(15) eV ~1.6 eV:

Mn V

0

8

Fe3+ relaxation rates- We find -1 T4(1)

- Theory suggests T2

- Similar inconsistency in ZnO [Mølholt et al., Phys. Scripta, 2011]

- Reason for this is unknown

1.E+00

1.E+08

2.E+08

3.E+08

4.E+08

5.E+08

6.E+08

100 200 300 400 500 600 700

τ-1(H

z)

Temperature (K)

cE2

01

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

100 1000

τ-1(H

z)

Temperature (K)

MgO, Al2O3: T2

ZnO: T9

9

Discussion/summary57Mn implantations into TiO2 single crystals and Mössbauer measurements on the daughter 57Fe A model of the annealing: VO stabilize Fe2+ state at T < 550 K VTi promote Fe3+ state at T < 330 K

VO-Mn(/Fe) dissociation energy Experimental (here) 1.60(15) eV Theory [Navarro11] ~1.6 eV

No defect related magnetism is found, but paramagnetism with “abnormal” temperature dependenceNo interstitial Fe displacement energy > 93 eV, consistent with theory (~130 eV [Thomas et al., 2005])